Huge landslide in Alaska park one of continent's biggest

ANCHORAGE, Alaska (Reuters) - A huge landslide in an Alaska park that went unnoticed for weeks turns out to have been one of the biggest on record in North America, National Park Service officials said on Thursday.

The slide spread rock and debris about 5.5 miles over a glacier in a remote section of Glacier Bay National Park in southeastern Alaska, officials said.

Unlike other landslides that have occurred in the past in the mountainous park, this event was not triggered by an earthquake, officials said.

"It was detected because of its magnitude, creating its own seismic event," said Lewis Sharman, a Park Service ecologist at Glacier Bay. Records at the U.S. Geological Survey show the event registering as having a magnitude of 3.4.

There were no people in the area at the time, and the slide was not seen until last week, when a Canadian air-taxi pilot flew over the site, said John Quinley, a spokesman for the Park Service's Alaska headquarters.

The slide was far from areas used by park visitors, most of whom tour Glacier Bay by cruise ship, Quinley said.

"You can't see it from a boat or the bay. You've got to be up flying. And it's not on a typical flying route," he said. "It would have been pretty horrific if you'd been camped on the glacier."

Sharman said it is not yet clear what caused the slide, which occurred on a flank of 11,924-foot (3,634-meter) Lituya Mountain. But experts believe that part of the slope simply gave way after repeated freeze-thaw cycles, he said.

Officials are currently trying to estimate the volume of material that fell in the slide, Sharman said.

Fifty-four years ago, there was a fatal landslide in Lituya Bay, which lies at the foot of a glacier flowing from Lituya Mountain.

A July 9, 1958 earthquake registering at magnitude 7.7 loosened massive amounts of rock that dropped into the bay, creating a wave that washed 1,720 feet up the narrow inlet, according to USGS records. Two people on a fishing boat vanished and were presumed dead, and three others on land were killed.